Fungi, together with bacteria and protists, are the major decomposers of organic matter on earth. Most fungi are saprobes
, that is, they digest nonliving organic matter, such as wood, leaves, and dead animals. However, some fungi are parasites that attack living things and cause disease. Fungi cause many agricultural diseases as well as several human diseases.
Some of those human diseases can be deadly. For example, a fungus called Cryptococcus neoformans infects the lungs and spinal cord. This disease is serious in AIDS patients because of their compromised immune systems.
Other fungal diseases that affect lung tissues include:
- Histoplasmosis. You'll find the fungus Histoplasma capsulatum in soil that's been contaminated with bird or bat droppings. Although the fungus grows around the world, it's most common in the Mississippi River and Ohio River Valleys.
- Blastomycosis. This respiratory infection is caused by airborne spores from the fungus Blastomycoses dermatitidis. Found mainly in the southeastern or south central United States, this disease is closely associated with activity (jobs or recreation) along rivers and streams — wherever you find high levels of moist, organic soil.
- Coccidioidomycosis. Commonly known as "valley fever," this disease is caused by a desert fungus called Coccidioides immitis. Desert winds carry the spores throughout the southwestern United States.
Another human pathogen is Candida albicans. This organism causes disease of the oral cavity (thrush), as well as "yeast disease" of the reproductive tract.
Human fungal diseases also can be just "skin deep." That is, they stay on top of your skin or in the uppermost layers of your skin. They aren't as serious as the lung ones but are kind of gross anyway. These include ringworm, jock itch, and athlete's foot. Each is caused by fungi of various genera, and each is characterized by blisterlike regions on the skin or in the webs of toes or fingers.